The present invention relates to a catalytic system which can be used for copolymerization of ethylene and a conjugated diene monomer, a method for preparation of this catalytic system, and a method for preparation of a copolymer of ethylene and a conjugated diene monomer, using the catalytic system.
It is known that ethylene may be polymerized using certain complex compounds based on lanthanides. These catalysts can be used over a wide range of pressures and temperatures, advantageously at a reduced pressure and a temperature which is close to ambient temperature, for the polymerization of ethylene.
The first complex compounds based on lanthanides described in the literature were alkylated complex compounds. In particular, in J. Chem. Soc., Chem. Comm. pp 994-995 (1978), Ballard et al. described the polymerization of ethylene by means of a complex compound corresponding to the formula [(C5H5)2ErMe]2 (in which Me is a methyl group).
These alkylated complex compounds can achieve instantaneous levels of activity which are very high, as described in U.S. Pat. No. 4,716,257, with reference to a similar complex compound corresponding to the formula [(C5Me5)2LnH]2 (in which Ln represents a lanthanide).
However, a major disadvantage of these alkylated complex compounds is that they are deactivated very quickly. Another disadvantage consists in the relative complexity of their synthesis.
In order to eliminate these disadvantages, there have been attempts to develop non-alkylated complex compounds which are based on lanthanides. These complex compounds have a metal-halogen bond and are alkylated in the polymerization medium. U.S. Pat. No. 5,109,085 describes the polymerization of ethylene with complex compounds having the formula CpnLnX4-nMxe2x80x2Lx (in which L is a complexing molecule, and x is a whole number equivalent to, or higher than 1), which have one or more co-catalysts added to them. The patent also refers to the possible use of the complex for copolymerizing ethylene and butadiene.
This type of non-alkylated complex compound has in its environment one or more complexing molecules L, which for example can consist of tetrahydrofurane or diethylic ether, and are added for reasons of organometallic synthesis.
However, it is found that these complexing molecules can compete with the ethylenic monomer during complexing on the lanthanide, with the undesirable consequence of limiting catalytic activity and, thus, the polymerization output.
In addition, Cui, Li Qiang et al: xe2x80x9cPreliminary investigations on polymerization catalysts composed of lanthanocene and methyl aluminoxanexe2x80x9d, Polymer Bulletin (Berlin), 1998, 40(6), pp 729-734, describe a catalytic system which is designed for homopolymerization of isoprene, butadiene, or styrene. This catalytic system comprises:
a rare earth organometallic complex compound in accordance with one or another of the following formula:
(C5H9Cp)2NdClxe2x80x83xe2x80x83(I);
(C5H9Cp)2SmClxe2x80x83xe2x80x83(II);
(MeCp)2SmOArxe2x80x2xe2x80x83xe2x80x83(III);
(Ind)2NdClxe2x80x83xe2x80x83(IV);
Me2Si(Ind)2NdClxe2x80x83xe2x80x83(V);
(Flu)2NdClxe2x80x83xe2x80x83(VI);
xe2x80x83in which Cp, Ind and Flu are respectively cyclopentadienyl, indenyl and fluorenyl groups, and OArxe2x80x2 is a phenoxy group; and
a co-catalyst consisting of methylaluminoxane, tested in comparison with a co-catalyst consisting of an aluminium alkyl.
The present invention provides an improved catalytic system for preparing copolymers of ethylene and a conjugated diene which do not have the aforementioned disadvantages of the art.
The present invention provides a catalytic system for copolymerizing ethylene and a conjugated diene comprising an organometallic complex compound represented by one of the following generic formula Axe2x80x2 or Bxe2x80x2: 
in which Ln represents a metal of a lanthanide, the atomic number of which is between 57 and 71;
X represents a halogen, selected from among chlorine, fluorine, bromine and iodine; wherein
in formula Axe2x80x2, two ligand molecules Cp1 and Cp2, which may be identical or different, selected from a substituted or unsubstituted cyclopentadienyl and fluorenyl group are bonded to metal Ln; and
in formula Bxe2x80x2, a ligand comprising Cp1 and Cp2 bonded to each other by a bridge P is bonded to metal Ln, wherein Cp1 and Cp2 comprise a substituted or unsubstituted cyclopentadienyl or fluorenyl group, bridge P corresponds to the formula MR2, in which M is silicon or another element of column IVA of Mendeleev""s periodic classification and R is an alkyl group having 1 to 20 atoms of carbon;
and a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminum alkyl, a Grignard""s reagent and mixtures thereof.
In a preferred embodiment metal, Ln is neodymium. Cp1 and Cp2 are preferably identical, each being a cyclopentadienyl group. More preferably, Cp1 and Cp2 are each a cyclopentadienyl group, substituted by an alkyl radical or a silyl alkyl radical.
The invention also provides for methods for preparing the catalytic system and its use thereof in preparing copolymers of ethylene and a conjugated diene.
The present invention provides an improved catalytic system for preparing copolymers of ethylene and a conjugated diene which do not have the aforementioned disadvantages of the art. The present invention provides a catalytic system for copolymerizing ethylene and a conjugated diene comprising an organometallic complex compound represented by one of the following generic formula Axe2x80x2 or Bxe2x80x2: 
in which Ln represents a metal of a lanthanide, the atomic number of which can be between 57 and 71;
X represents a halogen, selected from among chlorine, fluorine, bromine and iodine; wherein
in formula Axe2x80x2, two ligand molecules Cp1 and Cp2, which may be identical or different, selected from a substituted or unsubstituted cyclopentadienyl and fluorenyl group are bonded to metal Ln; and
in formula Bxe2x80x2, a ligand comprising Cp1 and Cp2 bonded to each other by a bridge P, is bonded to metal Ln, wherein Cp1 and Cp2 comprise a substituted or unsubstituted cyclopentadienyl or fluorenyl group, bridge P corresponds to the formula MR2, in which M is silicon or another element of column IVA of Mendeleev""s periodic classification and R is an alkyl group having 1 to 20 atoms of carbon;
and a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminum alkyl, a Grignard""s reagent and mixtures thereof.
In a preferred embodiment, Ln is neodymium Cp1 and Cp2 are preferably identical, each being a cyclopentadienyl group. More preferably, Cp1 and Cp2 are each a cyclopentadienyl group, substituted by an alkyl radical or a silyl alkyl radical.
Thus, in one aspect, the catalytic system of the invention comprises an organometallic complex compound, which is represented by one of formula Axe2x80x2 or Bxe2x80x2: 
in which Ln represents a metal of a lanthanide, the atomic number of which is between 57 and 71;
X represents a halogen selected from among chlorine, fluorine, bromine and iodine; wherein
in formula A, two ligand molecules CPA, each a substituted cyclopentadienyl group, are bonded to metal Ln;
and in formula B, a ligand, comprising two CpB, bonded to one another by a bridge P are bonded to metal Ln, wherein CpB is a substituted or unsubstituted cyclopentadienyl or fluorenyl group and P corresponds to formula MR2, in which M is an element in column IVA of Mendeleev""s periodic classification, and R is an alkyl group having 1 to 20 carbon atoms; and
a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminium alkyl, a Grignard""s reagent, and mixtures thereof.
In the case of substitution by a silyl alkyl radical, Cp1 and Cp2 each correspond to formula CpA=(C5H4)(SiMe3) in generic formula Axe2x80x2, or to formula CpB=(C5H3)(SiMe3) in generic formula Bxe2x80x2, where Me represents a methyl group. The organometallic complex compound then corresponds to particular formula A or B hereinafter, as applicable. 
In particular formula A, two molecules of CpA, each of which corresponds to formula (C5H4)(SiMe3) are bonded to metal Ln, and in particular formula B, a ligand molecule, comprising two molecules of CpB, each a substituted cyclopentadienyl group corresponding to the formula (C5H3)(SiMe3), bonded to each other by bridge P, is bonded to metal Ln.
In a further embodiment, Cp1 and Cp2 are identical, each comprising a non-substituted fluorenyl group which corresponds to formula C13H9, in generic formula Axe2x80x2, or which corresponds to the formula C13H8, for the said generic formula Bxe2x80x2. In the latter case, there corresponds to the formula Bxe2x80x2 the aforementioned particular formula B, in which CpB=C13H8.
If Cp1=Cp2=Cp, said organometallic complex compound is prepared as follows:
(a) preparing a hydrogenated molecule of ligand, represented by the formula HCp, which is reacted with a lithium alkyl to obtain a lithium salt;
(b) reacting the lithium salt in a complexing solvent with an anhydrous lanthanide trihalide, represented by formula LnX3, where X represents a halogen selected from among chlorine, fluorine, bromine and iodine to produce a reaction product;
(c) evaporating the complexing solvent, and extracting in a non-complexing solvent the reaction product of (b) to produce an extracted reaction product; and, optionally:
(d) crystallizing the extracted reaction product of (c), in order to obtain the organometallic complex compound which corresponds to formula A or B, which are completely free from the complexing solvent.
In step (a), lithium butyl is the preferred lithium alkyl.
In step (b), tetrahydrofurane (THF) is the preferred complexing solvent. In addition, two moles of the lithium salt are advantageously reacted with one or two moles of the lanthanide trihalide.
Toluene or heptane are preferred non-complexing solvents in step (c).
When the co-catalyst is a mixture of an aluminium alkyl and a lithium alkyl, these two components are advantageously present in quantities which are stoichiometric, or close to the stoichiometry in the mixture, in order to obtain satisfactory catalytic activity.
Preferred co-catalysts include magnesium butyloctyl, lithium butyl, aluminium diisobutyl hydride, magnesium butyl chloride and mixtures thereof.
In accordance with the invention, copolymers of ethylene and a conjugated diene are prepared by reacting the catalytic system comprising the organometallic complex compound and the co-catalyst with ethylene and a conjugated diene monomer in an inert hydrocarbon solvent.
Suitable conjugated dienes include 1,3-butadiene, 2-methyl 1,3-butadiene (hereinafter referred to as butadiene and isoprene, respectively), 2,3-di (C1 to C5 alkyl) 1,3-butadienes, such as 2,3 dimethyl-1,3 butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl 3-ethyl 1,3-butadiene, 2-methyl 3-isopropyl 1,3-butadiene, phenyl 1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, and any other conjugated diene having has between 4 and 8 carbon atoms.
The polymerization reaction can be carried out in suspension or in solution, at a variable pressure, and at a temperature of between xe2x88x9220xc2x0 C. and 220xc2x0 C., preferably between 20xc2x0 C. 90xc2x0 C.
The molar ratio of co-catalyst to organometallic complex compound is 1 or more, preferably 2 to 100.
The concentration of lanthanide in the reaction medium is advantageously lower than 0.3 mmole/l.
The molar fraction of butadiene in the reaction medium is advantageously between 1% and 80%.
With reference to Appendix I below, the copolymer of ethylene and a conjugated diene produced by the method of the invention can have the following microstructure characteristics, according to the organometallic complex compound used for the catalytic system.
If butadiene is the conjugated diene, the copolymer obtained can have the following chain formations for the butadiene units inserted in the copolymer:
1,4 cis; 1,4 trans; 1,2, or it can be in the form of trans 1,2 cyclohexane. (See Appendix I).
More particularly, when the organometallic complex compound corresponds to one of formulae [(C5H4)SiMe3]2NdCl, {[(C5H3)SiMe3]SiMe2}NdCl or (C13H9)2NdCl, most of the butadiene in the copolymer will comprise 1,4 trans chain formations.
When the complex compound corresponds to the formula [(C13H8)2SiMe2]NdCl, most of the butadiene in the copolymer chain will have a 1,2 trans cyclohexane configuration.
If isoprene is the conjugated diene, the copolymer obtained can have the following chain formations for the isoprene units inserted in the copolymer:
1,4; 1,2 or 3,4.
More particularly, when the organometallic complex compound corresponds to formula [(C5H4)SiMe3]2NdCl, most of the isoprene is inserted in the copolymer chain by 1,4 bonds chain formations.
When the complex compound corresponds to formula [(C13H8)2SiMe2]NdCl, most of the isoprene inserted in the copolymer by 3,4 chain formations.
A further characteristic of the ethylene and butadiene copolymers obtained by the method of the invention, is that they have an xe2x80x9cethylene-butadienexe2x80x9d chain formation statistic which is substantially of the alternating type, when the organometallic complex compound corresponds to Lima formula [(C5H4)SiMe3]2NdCl or formula {[C5H3)SiMe3]2SiMe2}NdCl, and a chain formation statistic that is substantially of the block type, when the complex compound corresponds to formula (C13H9)2NdCl. (See Appendix II below).
The aforementioned characteristics of the present invention, as well as others, will be better understood in view of the above description and the following non-limiting Examples 1-4 of embodiments of the invention compared to Example 5, which illustrates the prior state of the art.
For all of the following examples, the work was carried out using argon, and the solvents used were previously dried by distillation or on a 3 xc3x85 molecular sieve swept with argon.
The microstructure of the copolymers obtained in the examples was determined first by of RMN1H techniques, and second by the RMN13C technique. For this purpose, a spectrometer sold under the name xe2x80x9cBRUKERxe2x80x9d was used, at frequencies of 400 MHz for the RMN1H technique, and 100.6 MHz for the RMN13C technique.
Appendix I describes the method for determining of this microstructure.
Appendix II describes the method for determining xe2x80x9cethylene-butadienexe2x80x9d chain formation statistic.